Bluetooth and wirless interfering

When ever my bluetooth is turned on on my iMac, the wireless signal will either drop regularly or if not the internet will just be really slow. As soon as i turn it off no problem at all.
I have a wireless keyboard and mouse, but still have the problem if they are turned off.
I know that bluetooth and WLAN are on same frequency, however my router cannot be changed to 5.0 so is my only solution to get a new router?( i have tried changing channel)
Or does it sound more like a fault with the bluetooth as really i should be able to use both.
Thanks

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